Once considered old-fashioned and ungainly, rose of Sharon (Hibiscus syriacus) has regained its popularity in large part due to recent introductions from the National Arboretum. Varieties such as Diana and Aphrodite, with their larger flowers and more refined habit, have encouraged a new generation of gardeners to grow this dependable shrub. A light feeding twice a year is really the only attention rose of Sharon needs to grow well in most gardens.
Rose of Sharon Culture
Rose of Sharon is a tough plant. It thrives in full sun or light shade, in moist, well-drained soil high in organic matter, but it's so adaptable it grows well even in dry, compacted urban gardens. Rose of Sharon is rarely bothered by pests or diseases, although old shrubs develop stem cankers, a sign that the plant is declining and should be replaced with a new specimen. A heat lover, rose of Sharon is late to leaf out in the spring. It blooms on the current season's wood, so you can prune it heavily in early spring to control size or shape. Rose of Sharon is hardy in U.S. Department of Agriculture zones 5 to 8.
Choosing a Fertilizer
Rose of Sharon benefits from two different fertilizer formulations. For its spring feeding, use a light application of a balanced fertilizer such as 10-10-10 or 10-20-10. In midsummer give it a boost with a low-nitrogen fertilizer such as 0-10-10. Rose of Sharon is susceptible to bud drop and aphid infestations if over-fed, so be conservative with fertilizer amounts.
When to Fertilize
As with any deciduous shrub, rose of Sharon's initial spring feeding should be done after the plant has broken dormancy and the leaves are emerging, as this is the most effective time to fertilize. You can feed the plant in late fall or earlier in the spring, but those feedings are less effective, as the plant is not in active growth and some of the fertilizer nutrients will leach away before the plant absorbs them. Feeding the shrub a second time in midsummer with a low-nitrogen fertilizer encourages continued bloom production.
To prevent chemical burns to roots, the soil around any plant should be moist before you feed. If the weather has been dry, water the shrub well the day before you plan to fertilize. After applying a granular fertilizer, water again to move the fertilizer down into the soil. Always follow the package directions carefully for the correct amount of product to use. With fertilizer, more is not better.
If you're getting lots of leaf growth but few flowers, the shrub is either not getting enough sunlight or it's getting too much nitrogen. Make sure that lawn fertilizer is not being applied over the shrub's root zone.